Much of the epic progress during the industrial revolution in the United States during the 19th and 20th century was powered by steam. However, the thermal efficiency of steam powered piston engines could not match that of the Otto or Diesel engines developed at the end of the 19th century. A substantial improvement in steam engine efficiency was however made when the uniflow steam engine was developed by Professor Stumpf in Germany and improved further in the U.S. by C. C. Williams high compression uniflow engine based on compression as described in U.S. Pat. Nos. 2,402,699 and 2,943,608 in which steam is compressed to boiler pressure by the piston return stroke thereby raising the steam temperature for example 95 to 342 degrees hotter than feed steam in a sizeable clearance volume that may be 7% to 14.5% of displacement. The thermal efficiency of even these engines while improved, could not however reach that of the internal combustion engine.
Recently, a substantial advance has been made through the development of steam engines operating on a cycle that employs essentially zero clearance between the piston and the cylinder head at the end of the exhaust stroke while at the same time any steam in the cylinder is under little or no compression. This arrangement achieves a remarkable increase in thermal efficiency as disclosed in U.S. Pat. Nos. 8,448,440, 9,316,130, 8,661,817 and application Ser. No. 15/077,576 (now U.S. Pat. No. 9,828,866 B1) which are assigned to the Applicant's assignee and incorporated herein by reference. Engines in which both piston clearance and compression approach zero (the Z-Z operating principle) described in the patents noted provide a thermal efficiency which is from about 15% better to an extraordinary 59% better than the best performing high compression uniflow engines known (see FIG. 1). The outstanding efficiency of these engines relies in part upon the Z-Z operating principle and in part upon benefits arising from the use of a unique, fast acting inlet valve which can open fully in some embodiments in less than 1 millisecond thereby avoiding losses formerly caused by flow restriction through the inlet valve while the valve is being opened by a cam as in prior cam and eccentric operated engines in which the opening process may take as much as ⅓ to ¾ of a crankshaft rotation during which time the steam pressure rises relatively slowly in the expansion chamber causing a reduction in power output. By contrast, since the inlet valve of Z-Z engines and the present invention is opened almost instantly while the clearance is virtually zero, work output of the engine begins at steam supply pressure earlier in the cycle thereby providing more power without a compression loss. However, in the Z-Z engine patents and other engines using a bump valve, as the valve lifter on the piston makes physical contact with the valve to apply a lifting force a small impact occurs; but because the piston velocity falls to zero very close to when the lift takes place in the Z-Z patents only a few degrees before TDC with a small clearance of 0.020 inch, the impact of the lifter as it contacts the valve is acceptable in many applications but may not be acceptable in all applications.
Accordingly, it is one major aim of the present invention to retain the high efficiency and other advantages of the Z-Z engine patents noted above while finding a way to actuate valves by piston movement so as to avoid valve wear and noise as well as being able to operate valves rapidly, e.g., open the inlet fully in under 1 millisecond. By achieving these objectives in accordance with the present invention, the impact and associated shock wave characteristic of valves that are bumped open by piston contact are not simply reduced but are entirely eliminated along with the wear and clicking sound associated with prior valve lifters mounted on the piston, thereby rendering operation of the engines embodying the present invention very quiet while extending valve life almost indefinitely. Besides being quiet, the thermal efficiency of the engine described herein exceeds that of a steam turbine in medium to small sizes, especially those under 1000 horsepower and is lower in cost. These advantages make the invention particularly well-suited for applications such as electric power generation or the co-generation of heat and power as well as to power a vehicle or for use in solar power generation. A major advantage of the invention over internal combustion engines is the ability to use a variety of low grade fuels including waste or unrefined liquid fuels and biomass without producing harmful nitrogen compounds or other air polluting emissions generated by internal combustion engines.
In view of the deficiencies of the prior art it is one object to provide a way of actuating a steam inlet or exhaust valve by piston movement instead of a camshaft yet without producing an impact shock.
It is a more specific object to maintain the high thermal efficiency that characterizes the virtual zero or near zero pressure with zero clearance steam cycle of U.S. Pat. Nos. 8,448,440, 9,316,130 and pending application Ser. No. 15/077,576, now U.S. Pat. No. 9,828,866 B1 without the use of a camshaft for operating either a steam inlet or exhaust valve and without the need to actuate a valve by applying an opening pressure through physical contact with a valve.
A further object is to maintain the exhaust valve open throughout almost the entire exhaust stroke yet find a way to develop a sufficient inlet valve opening force without impact to at least partially open the steam inlet valve as the piston approaches the top dead center position.
Another object is to provide a method that enables piston movement to readily achieve the force needed to open a poppet type of inlet valve without the use of a camshaft or a need to apply physical contact to push the valve open.
It is still another object to actuate the valves in a way that provides high thermal efficiency by maintaining a small clearance between the piston and cylinder head at top dead center while expending little work in opening or closing valves as well as to avoid having to open the inlet valve against steam supply pressure.
Yet another object is to find a way to almost simultaneously open an inlet valve and close an exhaust valve without the use of either a camshaft or a valve lifter element for exerting an opening or closing force on a valve through physical contact.
Another object is to operate valves noiselessly without the use of a camshaft, yet be able to set inlet valve cutoff timing at any value needed as well as the ability to provide continuous variable cutoff regulation under changing loads if desired to achieve a higher overall thermal efficiency than heretofore possible in a reciprocating steam engine.
These and other more detailed and specific objects and advantages of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.